Electrical Engineering - Inductors - Discussion

Discussion :: Inductors - General Questions (Q.No.10)


An inductor, a 1 k resistor, and a switch are connected in series across a 6 V battery. At the instant the switch is closed, the inductor voltage is

[A]. 0 V
[B]. 6 V
[C]. 12 V
[D]. 4 V

Answer: Option B


No answer description available for this question.

Rajan said: (Mar 15, 2011)  
Why any current dropage is not there? There is one resistor is connected.

Mohsin said: (Jun 9, 2011)  
At t=0 inductor behave as open ckt and 6v dro across it.

Lipu said: (Feb 11, 2012)  
Then what is the volt across resister?

Sindu said: (Jul 28, 2012)  
As the nature of inductor is to oppose the change of current through it, it initially opposes the current flow through it. Thereby it acts as an open circuit. & total drop appears at inductor.

Sai said: (Sep 16, 2012)  
For dc inductor acts as a short cicuit. So voltage across inductor is zero.

Then how the voltage across inductor is 6v?

Henry said: (Nov 20, 2012)  
My first answer is also zero, but if you follow the principle behind resistance in series connection, V1=V2=V3=Vn, so 6v=voltage in resistor=voltage in inductor.

Uttam Kumar said: (Dec 11, 2012)  
Voltage drop = 0.

In DC network inductor works as short path. So no drop here.

The final answer is 0.0V.

Ramesh said: (May 22, 2013)  

In case of AC. Above answer is right as current cannot change instantaneously due to impedance.

But here battery is DC. Here inductor will act as a conductor (just like resistor). No ideal inductor exists. Ideal condition can be taken only for theoretical calculation as well as simulation purpose.

In real time. Inductor will offer some finite resistance to drop the voltage like resistor.

Since we have no idea about finite resistance in inductance. Hence we assume ideal condition 0V.

Anand said: (Dec 13, 2013)  
An inductor is does not allow sudden change in only current so voltage is supply voltage.

Soumya Sen said: (Feb 11, 2014)  
Here we are dealing with transient conditions. Hence answer is 6V.

Dinesh Diny said: (May 27, 2014)  
I agree with @Soumya sen. Here we're considering transient condition. Thus inductor is open. Hence voltage across inductor is 6V. Current=0 ==>voltage drop across resistor is 0.

Upendra said: (Dec 2, 2014)  
The inductor property is opposes to sudden changing current does not opposes voltage so total voltage appear across it.

Sharanappa said: (Mar 17, 2015)  
Current is given by i = I(1-e^Rt/L),

When t=0, i= 0,
Emf = L*di/dt.

So voltage is zero. Answer is A.

Santy said: (May 13, 2015)  
Though it is DC source. At 0 instant the voltage will bot be 6 V.

The voltage has to raise from 0 to 6 volts, which is change in voltage. This change is not acceptable by the inductor. Hence initially the inductor acts as a open circuit.

Manoj said: (May 27, 2015)  
For DC source inductor act as sort circuit the voltage is zero.

Hiren said: (Oct 27, 2015)  
Under transient condition (Here:-closing of switch) inductor behaves like open circuit so voltage across inductor is 6.

After than current in the circuit gradually increase and after finite time inductor behaves short circuit so that voltage across it 0.

Stuti said: (Feb 15, 2016)  
Here we know from transient analysis that when switch is on (t=0) then initially inductor behave like a open circuit. So no current flow through the circuit because of open circuit therefore no we drop across are and input we appear across L.

Rohul Amin said: (Apr 16, 2017)  
At t=0s ; f is infinite , and XL = 2pfL, hence XL is infinite.

Means open circuit.
Hence, the total voltage will be across an inductor and hence 6v.

Arka Ghatak said: (Apr 27, 2017)  
The Answer is 6v as there is no back EMF produced by the current in the inductor when we just close the switch.

Parth said: (Jun 24, 2017)  
As according to AC formula, V=Vm(1-e^-rt\L) for RL circuit the value of voltage at inductor will be zero, for the instant when switch is closed dc will behave same as AC.

Manish Singh said: (Oct 1, 2017)  
At instant, there is no change in current of inducter, so the current will for some time .

I=6/1=6 mA

After switch off current will remain same so the voltage will be
v=6*1=6 V.

Arun Reddy said: (Jan 6, 2019)  
As inductor doesnt allows sudden change in current. The voltage drop will be the same 6V.

Wendell A. said: (Jun 16, 2019)  
IN SERIES RL CIRCUIT Vs=VL x (e^-t/time constant).

If t=0 ; Vs= VL x e^0.

Therefore Vs=VL = 6V in t=0.

Neeraj Kumar said: (May 31, 2020)  
Here Voltage does not change.

Then, I= V/R=6/1000=0.006A.

And again R will not change because switch is off means R does not equal to zero,
Hence R=1000 ohm.

Then V =I * R = 0.006 * 1000,
= 6V.

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